1. Field of the Invention
This invention relates to a recording medium suitable for an ink jet recording process and particularly to a recording medium with a distinguished absorbability of aqueous ink and a good coloring property, capable of producing a considerably clear recorded image.
The present invention relates furthermore to a recording medium with less indoor discoloration of images, etc., capable of producing recorded images with a good preservation.
2. Related Background Art
Heretofore well-known recording mediums for the ink jet recording process include (1) plain paper composed mainly of pulps, processed into filter paper or blotting paper with a low sizing degree by a paper-making process, (2) high quality paper, etc. with less ink absorbability, provided with an ink-absorbing layer composed of porous inorganic pigments thereon, as disclosed in Japanese Patent Application Laid-open No. 56-148585, etc.
The ink jet recording system for forming a color image with a high grade and a high resolution requires particularly a better image preservability. In this connection, processes for retarding image color fading due to irradiation with sunlight, visible light, ultraviolet light, etc. are known {e.g. Japanese Patent Application Laid-open No. 60-49990, No. 61-57380 and etc.}.
Recently, a problem of indoor discoloration of recorded images has been newly addressed as a problem peculiar to coated paper. The problem of light resistance so far addressed has been a problem of image fading by irradiation with ultraviolet light or visible light, that is, a problem to be encountered on the images printed on any paper including ordinary PPC paper, i.e., high-quality paper, as well as coated paper for ink jet printing. The problem of image indoor discoloration as mentioned above is a problem of discoloration of images formed on coated paper preserved at locations without direct exposure to sunlight, and is not encountered on the images printed on non-coated paper such as PPC paper, etc. That is, the problem of image indoor discoloration is another problem than that of light resistance. Thus, the problem of image indoor discoloration is peculiar to coated paper and thus seems to be due to pigments that constitute the coating layer. It is known that image indoor discoloration is connected to the specific surface area of the pigments used, and image indoor discoloration can be suppressed with ordinary fillers of small specific area such as calcium carbonate, kaolin, talc, etc. However, the optical density is low when such a filler is used, and images with a high quality and high resolution are hard to obtain. In other words, images with a high optical density can be obtained on coated paper using silica of large specific surface area and high activity, as disclosed, for example, in Japanese Patent Application Laid-open No. 56-185690, whereas the problem of image indoor discoloration becomes remarkable. As explained above, the suppression of image indoor discoloration and the increase in optical density are inconsistent with each other, and the inconsistency has not been solved so far.